Carrier current control system



March 3, 1942.

H. E. HERSHEY CARRIER CURRENT CONTROL SYSTEM Filed April l, 1939 2SheeiZs--Shee'fl l Harry- E Hers/1e y BY M ATTORNEY 5.

March 3, 1942. H. E. HERSHEY CARRIER CURRENT CONTROL SYSTEM Filed Aprill, 1939 2 Sheets-Sheet 2 cn O3 Tl l BY /avw INVENTOR. y Harry E Hers/:eg,15:27, MM,

ATTORNEYS.

Patented Mar. 3, 1942 CARRER CURRENT CONTROL SYSTEM Harry E. Hershey,Chicago, Ill., assigner to Associated Electric Laboratories, Inc.,Chicago, Ill., a corporation of Delaware Application April 1, 1939,serial No. cette:

(o1. iiiasin 1i) Claims.

'I'he present invention relates to carrier current systems and, moreparticularly, to improvements in systems wherein a power transmissionline or the like is utilized as a control channel between a transmittingpoint and a plurality of control points. Carrier current apparatusutilizing power lines as carrier links has been extensively used forcommunication and control purposes and has been found to have particularutility in controlling from a central dispatcher-S station theconnection of heater loads or the like to the power lines.

It is an object of the present invention to provide an improved systemof the character indicated which is of simple and economicalarrangement; is reliable in operation and is arranged in an improvedmanner such that a large number of circuits or devices, such, forexample, as water heaters, may be controlled from a central dispatchingor transmitting point with a minimum amount of apparatus.

It is another object of the invention to provide, for use in a system ofthe character described, an improved carrier current transmitting unitwhich utilizes a minimum amount of apparatus; is simple in arrangement;is reliable in operation and is easily operated selectively to controlover a single associated carrier channel any one of a plurality ofcarrier current receiving units each having associated therewith aplurality of devices or circuits to be controlled.

It is a further object of the invention to provide, for use in a systemof the character described, an improved transmitting unit of simple andeconomical arrangement which may selectively be controlled by anattendant to select and control over an associated control channel anydesired one oi a plurality of associated circuits or devices theenergization or deenergization of which may be required.

In general, the objects as set forth above are realized in accordancewith the present invention by providing carrier current apparatus forcontrolling a plu ,-ty of secondary carrier current circuits arranged ingroups, comprising a transmitter and a plurality of receivers which areinterconnected by a carrier current channel so that the receivers arecontrolled over the channel from the transmitter in a novel and uniquemanner. More iiiticu the transmitter includes a c c. a circuit fordelivering current from sel-roe to the carrier current channel, andincluding an impnlsing device for meiner. 'ily .iterrupting the deliverycircuit one or more 'times during CAB each operation of the impuisingdevice thereby to transmit carrier current pulses by way of the channelto the various receivers. The transmitter further includes timingapparatus, the operation of which is initiated in response to operationof the impulsing device, and circuit means controlled by the timingapparatus for interrupting the carrier current delivery circuit after apredetermined time interval. The timing apparatus is so arranged thatits operation is only initiated after a predetermined number ofoperations of the impulsing device and the operation thereof issustained through the provision of relay means operable independently ofthe impulsing device following the initial operation of the timingapparatus. The arrangement of the transmitter is such that the timingapparatus may measure off either of two time intervals, during whichcarrier current is conducted to the associated carrier channel.v Thedesired interval is selected through the selective operation of a pairof switches representing, respectively, heaters on Iand heaters off, andthe provision of circuit means jointly controlled by these two switchesand the timing apparatus for interrupting the carrier current deliverycircuit at the end of the time interval corresponding to the operatedone of the two switches.

The carrier current receivers commonly associated with the carriercurrent channel are each associated with a plurality of secondarycarrier circuits which are to be controlled and each thereof includesapparatus responsive to a first predetermined digit of carrier currentpulses transmitted over the carrier channel for conditioning itself toselect one of the associated secondary carrier circuits. This apparatus,as embodied in each receiver, is responsive to a rst digit other thanthe predetermined digit designating the receiver to render the receiverineffective to select one of its associated circuits or, moreparticularly, to render the receiver non-responsive to f additionalcarrier current pulses transmitted over the carrier channel. Eachreceiver further comprises apparatus responsive to a second digit ofcarrier current pulses transmitted over the associated channel followingthe predetermined iirst digit for selecting one of the associatedsecondary carrier circuits, together with circuit means controlled bythe last-named apparatus for operating upony i. e., for completing orinterrupting the selected circuit. More particularly, each receiverincludes a stepping switch vidually corresponding to the associatedsecondary carrier circuits and pulse responsive apparatus which respondsto a received rst digit of carrier current pulses to cause the switch tooperate to the position corresponding to the number of pulses of thedigit. When each of the switches operates to a predetermined position(different for` each of the receivers), the control apparatus associatedtherewith is conditioned for the selection of one of the associatedcircuits. On the other hand, if the switch is operated to any otherposition, it is rendered non-responsive to further operation of thepulse responsive apparatus. After being conditioned to respond to asecond series of received carrier current pulses, each stepping switchand its associated control apparatus operates to select one of theassociated secondary carrier circuits when the second digit of carriercurrent pulses is received. Thereafter, the control apparatus of thereceiver functions to interrupt or complete the particular selectedcircuit. Each receiver is so arranged that when carrier current isremoved from the channel over which it is controlled, the receiver isreleased and the operated control device is restored to normal.

Further features of the invention pertain to the particular arrangementof the circuit elements whereby the above-outlined and additionaloperating features are attained.

The novel features believed to be characteristic of the invention areset forth with particu'larity in the appended claims. The invention,both as to its organization and method of operation, together withfurther objects and advantages thereof, will best be understood byreference to the specification taken in connection with the accompanyingdrawings in which Figures 1 and 2 illustrate, respectively, atransmitter and a plurality of lreceiving units connected and arrangedin accordance with the present invention and interconnected by a carriercurrent channel.

Referring now to the drawings, the system there illustrated comprises atransmitter as shown in Fig. 1 and a plurality of receivers, two ofwhich are shown in Fig. 2; the transmitter and receivers beinginterconnected by a carrier current channel which includes one conductorI!) of a power transmission line and a ground return path. If desired asecond of the power line conductors may be used in lieu of ground toprovide a complete carrier current channel. The carrier current outputof the transmitter shown in Fig. 1 is irnpressed upon the carriercurrent channel comprising the conductor Ill and ground by meanscomprising a coupling unit II and a transformer I2. At each receivingstation a coupling unit similar to the unit I I is provided forfiltering the carrier current from the commercial frequency current andfor delivering the filtered carrier current to the associated receiver.Thus, the receiver I3 and the other receiver illustrated in detail inFig. 2 have individually associated therewith coupling units i4 and l5,respectively, which function to filter the carrier currents from thecommercial frequency current and to deliver the ltered output to therespective associated receivers. Each of the coupling units II, llt, andI5 may be of any desired arrangement. Since several well-knownembodiments of this type of apparatus are commercially available, theseelements of the system have been only schematically shown.

Referring now more particularly to the transmitting apparatus as shownin Fig. 1, this apparatus includes a source of carrier currentcornprising an alternator I6, arranged to deliver its high frequencyoutput over an obvious circuit to the primary winding of a transformerI2 and to be driven by an alternating current motor Il which ispreferably of the self-starting synchronous type. The motor Il alsofunctions to drive a self-excited direct current generator I8 whichdelivers exciting current to the slip rings of the generator I (i overan obvious circuit including the adjustable field rheostat I9. Thisgenerator may also be utilized to supply current for energizing thevarious relays, magnets and signal lamps of the transmitter. To thisend, the armature leads of the generator I8 are connected to busterminals i9 and 20 which may, in turn, be connected over b-usconductors to appropriate terminals of the indicated circuit elements.In the interests of simplifying the circuit explanation, these busconductors have been omitted from the drawings but it will be understoodthat the negative terminal 2i) is connected to each of the otherterminals shown in Fig. 1 of the drawings marked with a negative batterysign and that the positive terminal I9 is similarly connected to each ofthe terminals designated by a positive battery sign. For the purpose ofinitiating the operation of the motor l?, there is provided a start keyor switch 2 I, which switch also functions to control the operatingcircuit for a signal lamp 22 provided for the purpose of reminding thetransmitter attendant or dispatcher that the switch 2| is operated.

The circuit for delivering carrier current from the alternator i6 to thecarrier channel comprising the power line conductor Il) and ground isarranged to be controlled by an electromagnetic device in the form of apulsing relay` or contactor 25 which is operative in response tooperation of either of two key controlled switches 2'I and 28. Moreparticularly, the operating circuit for the pulsing relay 25 iscompleted in response to operation of either of two relays 3l) and 40which respectively respond to operation of the switches 2l and 28. Theserelays also individually control the operating circuits for a pair ofsignal lamps 23 and 24, the lamp 23, when energized, functioning toindicate that the relay 3l] is operated and the lamp 2li, whenenergized, functioning to indicate that the relay 40 is operated. Theswitches 2'! and 28 selectively control the time interval during whichcarrier current is delivered to the carrier current channel andrepresent, respectively, heaters on and heaters off time intervals. Eachof these switches is of the well-known nonlocking type. Theabove-mentioned operating circuit for the pulsing relay 25 also seriallyincludes the pulsing springs Se of an impulsing device 35. Thisimpulsing device is of the dial operated type conventionally used inautomatic telephone systems and is capable of transmitting from one toten impulses during each voperation through selective operation of thedial embodied therein. In

lgie set of contacts 5I of twenty-five points, a

double-ended wiper 52, and means comprising a motor magnet 53 and aratchet and pawl mechanism, not shown, for driving the wiper 52 over thecontacts of the set The mechanical arrangement of the ratchet and pawlmechanism is such that the wiper 52 is advanced only upon deenergizationof the magnet 53 following its energization. Operation of the switchfrom its normal position as shown in the drawings is initiated inresponse to operation ofy the impulsing device 35. For the purpose ofsustaining the operation of this switch following its initial orpreliminary movement, there are provided a pair of relays |53 and 65;the first-mentioned being of the slow-to-operatc type and thelast-mentioned being of the well-known pendulum type. More particularly,the relay includes a weighted armature 66 which vibratcs when the relay65 is initially energized and only settles into resting engagement withits associated contact a predetermined time interval thereafter. Theswitch 50 is arranged to control a relay l5 which is provided for thepurpose of causing the carrier current output of the generator It to beremoved from the carrier channel a predetermined time interval afteroperation of the switch 5i) is. initiated.

More particularly, the relay i9 is jointly controlled by the switch 5Band the relays 3Q and 40 to cause the pulsing relay 25 to restore apredetermined time interval after operation oi the switch 50 isinitiated, providing the switch Z1 is operated, or to cause therestoration, of the pulsing relay 25 after the expiration of a longertime interval in the event the switch 28 is operated. f,

In order to cause the carrier current delivery circuit to be interruptedbefore either of the two indicated time intervals have expired and inthe event of a dialing error on the part of the dispatcher, there isprovided an error key 'l5 which, when operated, functions to complete anormalizing circuit for the rotary switch 5i), thereby to cause thisswitch to be returned to its normal position at a high rate of speed.

Referring now more particularly to Fig. 2 of the drawings, the tworeceivers there shown are, with the exception of certain wiringdifferences, exact duplicates. Accordingly, only one of the receivershas been illustrated in detail. The lastmentioned receiver functions tocontrol ten associated circuits, one of which is indicated generally at19. Each of these ten circuits is adapted to be energized by carriercurrent and may be utilized directly to control an associated controldevice or to control such a device over a secondary carrier channel. Forexample, if the circuit 19 is to be used in an application ofthecharacter previously mentioned, that is, for the purpose ofcontrolling the switching unit associated with an electric water heater,the switching unit may be directly connected to the bracketed terminalsof the circuit 'i9 or may be coupled to these terminals over a carrierchannel utilizing one or more of the secondary power leads` If desired,the control device which is controlled over the circuit 'I9 and theother similar circuits may be of the character disclosed in Patent No.2,664,644, granted December' 15, 1936, to John L. Woodworth. Asexplained in this. patent, when the control device disclosed therein isenergized by carrier current for a relatively short time interval, thedevice operates to close the power supply circuit of 'the associatedheater, On the other hand, wheny the control device is energized bycarrier current for a relatively long time interval, it is operated toopen the associated power supply circuit and to maintain this circuitinterrupted until it is thereafter energized by a short pulse of carriercurrent. Briefly described, the receiver illustrated in detail in Fig. 2comprises a rectifier to which carrier current is delivered throughcoupling unit I5 and which functions to convert the carrier current intodirect current for energizing the combined start and pulsing relay 35.If desired, the rectifier 80 may be of the well-known Vacuum tube typeutilizing one or more stages of amplification for the purpose ofincreasing the amplitude of the received carrier current suiciently toinsure positive response of the relay 85. In order to energize anyselected one of the above-mentioned secondary carrier current circuits,there is provided at the receiving station a carrier current sourcewhich comprises a high frequency alternator S1 arranged to be driven byan alternating current motor 88, preferably of the self-startingsynchronous type. The motor 83 is also mechanically coupled to drive aself-excited direct current generator 8d which functions to deliverexciting current through an adjustable field rheostat to the slip ringsof the alternator 01. It is also contemplated that the generator 39shall be used to supply energizing current to the windings of thevarious relays and magnets embodied in the receiver. To this end, thepositive and negative lterminals JI and 92, respectively, of thegenerator 89 are connected by means of bus conductors, not shown, to therespective positive and negative terminals of the relay and magnetwindings shown in Fig. 2 of the drawings. The alternating current motor88 is adapted to be energized from the usual volt alternating currentsource and includes an operating circuit which is controlled by analternating current relay or contactor 95. This contactor, in turn, iscontrolled by an alternating current relay 91 having a winding adaptedto be connected in shunt with the secondary winding 99 of a voltagereducing transformer |00 in series with a condenser |0|, in response tooperation of the combined start and pulsing relay 85.

For the purpose of selecting one of the ten associated secondary carriercircuits, there is also provided in the receiver illustrated in Fig. 2 acircuit selecting switch |05 and control apparatus comprising aplurality of relays |30, |40, |50, |50, |10, |83 and |90. Moreparticularly, the switch |65 is of the well-known rotary type andcomprises four sets of contacts |06, |01, |08 and 09, each comprisingeleven contacts; wipers |'|0, H2 and ||3 respectively associated Withthe contact sets in the order named; means comprising a motor magnet 1|and a ratchet and pawl mechanism, not shown, for driving theindcatedwipers over their respectively associated contacts; and a set ofoff-normal springs ||5 which are moved into engagement when the wipersof the switch are stepped to the first offnorinal position from thenormal position illustrated in the drawings, Of the enumerated relays,the relay |30 is a highly sensitive pulsing relay which responds toopera-tion of the combined start and pulsing relay 85; the relay |40 isa slow-acting hold relay; the relay |50 is a slave to the relay |559 andthe relay |60 is a slowacting pulsing digit responsive relay. Of theremaining three relays the relay lili) is provided for the purpose ofrendering the switch |05 responsive to a second digit of receivedcarrier current pulses following the receipt of a rst digit designatingthe receiving unit under consideration as the one receiver which is toeiect a circuit controlling operation. This relay further functions tocause the wipers of the switch |55 to be returned to normal during theinter-digit pause between two successively received digits, The relay|33, in combination with the slow-to-operate relay Htl, functions toopen the operating circuits for themotor magnet Ht at the end of areceived second digit of carrier pulses, thereby to render the receivernon-responsive to additional pulses received after a circuit selectingoperation has been performed. In this regard it is pointed out thatcontrol of the ten secondary carrier circuits associated with thereceiver is achieved through the provision of ten control devices, oneof which is indicated at Eii, which individually correspond to the tenoperating positions of the switch m5 and individually include operatingcircuits extending by way of different ones of the contacts embodied inthe contact set |99 of the switch H35. The manner in which theseoperating circuits are selectively completed will be more readilyapparent from the descrip tion of the operation of the apparatusappearing hereinafter.

Referring now more particularly to the operation of the system, if it beassumed, for example, that the control device controlled by way of thesecondary carrier circuit 'i9 occupies its open circuit position, and,further, that the dispatcher or attendant desires to effect operation ofthis control device to close the associated heater or load circuit, theswitch 2| is rst operated to its off-normal position and shortlythereafter the switch 2l is also operated to its off-normal position.When the switch 2| is operated to its off-normal position, obviouscircuits are completed for energizing the motor il and the signal lamp22. As the motor il cornes up to speed, the voltage across the terminalsi9 and 25 of the generator i3 builds up to normal so that with the iieldrheostat le properly adjusted the correct exciting current is suppliedto the rotor of the alternator i6. Accordingly, the carrier voltage ofthis generator builds' up to the normal value in the usual manner.Following the interval required for the motor il to assume its normalspeed, the switch 21 is momentarily operated to its off-normal positionto complete an obvious w circuit for energizing the relay 3d. Uponoperating, the relay (it completes, at its armature 3|, an obviouscircuit for energizing the signal lamp 23 and closes, at its armature32, a circuit including the armature 'H for maintaining itself energizedindependently of the switch 2l. Hence, momentary operation of the switch2l suffices to initiate the operation of the transmitter. Uponoperating, the relay 3e also completes the abovementioned circuit forenergizing the Winding of the pulsing relay or contactor 25, thiscircuit eX- tending from the positive terminal i9 of the generator IS byway of the winding of the relay 25, the armature 33 and the impulsingsprings @t to the negative terminal 26 of the generator I8. Whenenergized over this circuit, the relay Z5 opcrates to complete at itsarmature 26 the circuit for energizing the primary winding of thetran."- former l2 from the alternator it. Thus, carrier current voltageis impressed upon the carrier channel comprising the conductor it andground, which channel extends from the transmitter to each of thereceivers controllable from the transmitter.

y The rectifier 8U provided in the receiving unit illustrated in detailin Fig, 2 responds to the carrier current voltage impressed upon thecarrier channel by delivering direct current to the Winding of thecombined start and pulsing relay 85. The relay 85 now operates tocomplete, at its armature 8, a circuit including the transformer Winding99 and the condenser for energizing the alternating current relay Sl.The relay Sl, in turn, operates to complete at its armature 98 anobvious circuit for energizing the Winding of the contacter 95. Thiscontactor, upon operating, completes at its armature 96 an obviouscircuit or energizing the alternating current motor 88. As the motor 88comes up to speed, the normal output voltage of the direct currentgenerator 89 is built up across the generator terminals 9| and 92 andiield current is supplied to the rotor of the alternator 87. Thus, thecarrier voltage output of the alternator 87 is built up to its normalvalue. When the voltage of the generator 39 assumes its normal value,the relay I 30 is energized thereby over a circuit extending from thepositive generator terminals 9| by way of the armature 85 and thewinding of the relay 13|] to the negative generator terminal 92. Whenthus energized, the relay ISE! operates to complete at its armature |3|an obvious circuit for energizing the slow-acting hold relay Mii. Thelast-mentioned relay, in turn, operates to complete at its armature |4|an obvious circuit for energizing the relay |59. When the relay |58operates, it prepares at its armature |5| a circuit for energizing theslow-acting relay |68 and the motor magnet H4 in parallel. At itsarmature |52, the relay |50 prepares a point in the common portion ofthe holding and operating circuits, traced hereinafter, for the relays|70, IES and ISS. At its armature |53, the relay |56 completes anobvious multiple circuit for maintaining the contactor 95 operated.Finally, at its armature |511, the relay |50 prepares a point in thecommon portion of the operating circuit for the control device 200 andthe operating circuits for each of the other nine control -devicesassociated with the receiver. Following the operation of the relay lil,the receiver illustrated in Fig. 2 is conditioned to respond to carriercurrent pulses transmitted by way of the carrier channel from thetransmitter shown in Fig. l in response to operation of the impulsingdevice 35,

vWhile the operation of the receiver shown in detail in Fig. 2 has alonebeen described, it will be understood that each of the other receiversassociated with the carrier channel comprising the conductor lil andground responds to the application of carrier voltage to this channel inan identical manner` A short time interval after operation of the switch2l, and shortly following the completion of the receiver operations justdescribed, the transmitter attendant operates the impulsing device 35inaccordance with the digit designating the receiver associated with thegroup of circuits including the particular circuit which is to'be oper`armature 34, the shunt springs 31 andthe Winding of the magnet 53 to thenegative generator terminal 20. When energized over this circuit, themagnet 53 conditions the associated ratchet and pawl mechanism, notshown, to step the Wiper 52 one step from its normal position as y shownin the drawings. During the return movement of the dial embodied in theimpulsing device 35, the pulsing springs 30 are opened and closed anumber of times determined by the number of the -digit dialed. In thecase under consideration, these springs are opened and closed six times.Each time the springs 36 are moved out of engagement, the above-tracedoperating circuit for the relay 25 is interrupted, causing this relay torestore and open at its armature 2S the circuit over which carriercurrent is delivered to the carrier current channel. Accordingly, duringthe first operation of the impulsing device 35, six carrier currentpulses are tran-smitted over the channel to each of the receiversassociated therewith. At the end of the sixth impulse, the dial of theimpulsing device 35 is fully restored to normal, so that the springs 36are closed and the shunt springs 37 are moved out of engagement tointerrupt the above-traced circuit for energizing the magnet 53. As aconsequence, the ratchet and pawl mechanism associated with the magnet53 operates to advance the wiper 52 one` step from normal or intoengagement with its associated first contact,

Considering now the manner in which the receiver illustrated in detailin Fig. 2 responds to the carrier current pulses of the first digitdialed at the transmitter, it is pointed out that the relay 85 followsthe carrier current pulses by restoring during each interval when thecarrier current delivery circuit is interrupted at the transmitter.Accordingly, it will be seen that the relay 85 functions to repeat thecarrier current pulses as direct current pulses to the pulsing relay|30, the relay |30 being caused to restore each time the carrier currentdelivery circuit is interrupted at the transmitter. Upon restoring atthe beginning of the first pulse, the relay |30 completes theabove-mentioned circuit for energizing the slow-acting relay |60 inparallel with the motor magnet HG of the rotary switch |05, this circuitextending from the positive generator terminal 9| by way of the armature|3| lto the armature ii where it divides; one branch extending throughthe winding of the relay |60 to the negative generator terminal 92, andthe other branch extending by way of the armature |1| and the winding ofthe magnet ||4 to the negative generator terminal 92. When energizedover the circuit just traced, the relay |60 operates to open at itsarmature IGI a point in the circuits, traced hereinafter, for energizingthe relays and |90, respectively. At its armature |62, the relay |60opens a point in the common portion of the circuits for energizing thecontrol devices corresponding to and including thedevice 200.

Each time the relay |30 restores in response to a received carrier pulseto complete the abovetraced circuit for energizing the motor magnet H4,this magnet in cooperation with its associated ratchet and pawlmechanism, not shown, operates to advance the wipers of the switch |05one step. Accordingly, at the end of the first digit, these wipers areleft standing in engagement with the contacts corresponding to thenumber of pulses of the digit. The relay |50,

due to its slow-to-release character, remains operated during pulsing.When the wipers of the switch |05 are operated to their respective firstoff-normal positions, the off-normal springs H5 are moved intoengagement to prepare a circuit, traced hereinafter, for energizing theslow-to-operate relay |70. In the case under consideration wherein therst digit dialed comprises six carrier current pulses, the wipers theswitch |05 are left standing in engagement with their respectivelyassociated sixth contacts. Shortly following the end of this digit andwith the relay |30 in its operated position, the slowacting relay |00restores to complete the abovementioned circuit for energizing the relay|90, this circuit extending from the positive generator terminal 9| byway of the armature |52, the armature ll, the wiper ||2 and itsassociated sixth contact, the contact |95, the armature` |93, and thewinding of the relay |90 to the negative generator terminal 92. Whenenergized over the circuit just traced, the relay |90 operates tocomplete a ho-lding circuit for itself, this ircuit extending from thepositive generator terminal 9| by way of the armature |52, the armature|9, the armature |93, and the winding .of the relay |90 to the negativegenerator terminal 92. Also, upon operating, the relay |90 opens at itsarmature |96 a point in the circuit, traced hereinafter, for energizingthe slow-tooperate relay |70, and prepares at its armature |92 avcircuit for energizing the relay |00. At its armature |9I, the relay |90completes an alternative circuit for energizing the motor magnet H4,this circuit extending from the positive generator terminal 9| by way ofthe armature lei, the armature ISI, the multipled contacts of theContact set |06, the wiper H0, the armature |6 and the winding of themagnet I4 to the negative generator terminal 92. Due to the circuitinterrupting action of the armature HG controlled by the magnet H4, thismagnet operates buzzer fashion rapidly to restore the Wipers of switch|05 to normal at which time the off-normal springs ||5 are opened. Whenthe wiper ||0 attains its normal position in engagement w'ith itsassociated eleventh Contact, the above-traced normalizing circuit forthe switch |05 is interrupted. The return of the switch wipers to normalalso results in energization of the relay over a circuit extending fromthe positive generator terminal 9| by way of the armature |52, the wiper||I and its associated eleventh contact, the armature |92 and thewinding of the relay |80 to the negative generator terminal 92. Uponoperating, the relay I80 completes, at its armature |82, an obviouslocking circuit for itself, and opens, at its armature ISI, a furtherpoint in the abovetraced switch normalizing circuit. At its armature|83, the relay |80 prepares the abovementioned circuit for energizingthe slow-tooperate relay |10. Following operation of the relay |80, theapparatus embodied in the receiver illustrated in detail in Fig. 2 ofthe drawings is conditioned to respond to a second series of carrierpulses` transmitted thereto from the transmitter shown in Fig. 1 of thedrawings.

The circuit group or receiver selection achieved in response to thefirst digit dialed at the transmitter is obtained by connecting therelays, corresponding to the relay and included in the other receivers,to be energized in response to operation of their respectivelyassociated rotary switches to different oir-normal positions. In thisregard, it Will be clear from the preceding current pulses.

description that the rotary switches respectively embodied. in theseveral receivers are operated in unison in response to the carriercurrent pulses of the first digit. Only the relay |99 of the receivershown is, however, connected to be energized when the wipers of theseswitches are left` standing in engagement with their respectivelyassociated sixth contacts at the end of the first digit. rThecorresponding relays of the other re- -ceivers are connected to beenergized when the 1operated to its second off-normal position inresponse to the carrier current pulses of the first digit. As a furtherexample, a third of the receivers may be so connected and arranged thatthe relay embodied therein and corresponding to the relay tilt isenergized following the trans-- mission of a rst digit comprising threecarrier By virtue of this arrangement, any one of ten differentreceivers may, with the arrangement shown, selectively be conditioned torespond to the carrier pulses resultingfromthe dialing of a second digitat the transmitter.

To illustrate the manner in which a receiver is rendered non-responsiveto further carrier current pulses when a first digit other than thedigit designating the receiver is dialed at the transmitting station,the response of the receiver illustrated in Fig. 2 to a iirst digitcomprising three impulses may be considered. In this case, the wipers ofswitch are left standing in engagement with their respectivelyassociated third contacts at the end or the digit. Accordingly, theoperating circuit for the relay i90 is not completed. Since this relayfails to operate, the operating circuit for the slow-to-operate relay llis energized for a substantial time interval during the inter-digitpause between the rst and second digits. This circuit is completed inresponse to the restoration of the relay It@ and may be traced asextending from the positive generator terminal 9i by way of the armature|52, the armature IGI, the off-normal springs H5, the armature igt andthe winding of the relay l'l to the negative generator terminal S2.After an interval following the completion of this circuit, the relayGili operates to complete, at its armature |72, an obvious holdingcircuit for itself. At its armature lli, the relay Il'El opens a pointin the above-traced circuit for energizing the motor magnet Hd of therotary switch |55. Thus, this rotary switch is rendered non-responsiveto further carrier current pulses transmitted to the receiver. Since therelay lil fails to operate, the wipers of the switch H35 are leftstanding in their third off-normal positions until carrier current isremoved from the carrier channel to initiate the release of thereceivers in the manner explained subsequently. Since the operatingcircuit for the relay 59S extends only by way of the sixth contact ofthe contact set itt, it

will be apparent that the operations just described occur in any casewhen a iirst digit other than the digit six is dialed at thetransmitter. It will further be apparent that since any one of tendifferent digits comprising from one to ten pulses may be dialed atthevtransmitter any one of-ten different receivers may be conditioned,

. energized by way of the tenth Contact of the conto the exclusion ofall of the other receivers, to respond to the pulses of the seconddigit.

The character of the second digit dialed at the transmitter depends uponthe particular one of the secondary carrier circuits which is to beoperated upon. In the present case wherein the circuit i9 is to becompleted and the control device 29 associated with this circuit canonly be tact set |59, a second digit of ten impulses is dialed at thetransmitter. The receiver illustrated in Fig. 2 of the drawings respondsto the carrier current pulses of the second digit in a mannersubstantially similar to that just described with reference to thecarrier current pulses of the iirst digit. More particularly, the relay113B follows the carrier current pulses and transmits correspondingpulses to the motor magnet ||li of the switch i5 so that the wipers ofthis switch are advanced to the oit-normal position corresponding to thenumber of pulses making up the second digit. Also, the relay it@operates at the beginning of the iirst pulse of the digit and due to itssloW-to-release characteristic, remains operated until the digit isended. Further, the off-normal springs H5 are closed to prepare thecircuit for energizing the relay |75 when the wipers of the switch |65are operated to their respective first orf-normal positions. In thepresent case wherein ten carrier current pulses are transmitted to thereceiver during the dialing or" the second digit, the lwipers of theswitch |55 are left standing in engagement with their respectivelyassociated tenth contacts when the digit is terminated. Shortly afterthe last carrier pulse is received and with the relay |36 operated, therelay It@ restores to complete an alternative circuit for energizing theslow-tcoperate relay |15, this alternative circuit extending from thepositive generator terminal 9| by way of the armature |52, the armaturell, the oli-normal springs ||5, the armature |83, and the winding of therelay |79 to the negative generator terminal 92. Upon restoring, therelay |50 also completes the operating circuit for the control device260 associated with the selected secondary carrier circuit 79. Thiscircuit may be traced as extending from one terminal of the alternatingcurrent source by way of the winding of the control device Zim, thetenth Contact of the contact set |69, the wiper |53 and the armatures|84, |62, and |54 to the opposite terminal of the alternating currentsource. When energized over this circuit, the control device 298operates to complete at its armature 20|, the secondary carrier circuitI9, whereby the switching unit terminating this carrier circuit isenergized by the carrier current output of the alternator 8l. Followingthe operation of the control device 260, no further operations occur inthe receiver until carrier current voltage is removed from the carrierchannel comprising the conductcr I!! and ground.

During operation of the impulsing device 35 to cause the second digit often carrier pulses to be transmitted over the carrier channel, the shuntsprings 31 aremoved into engagement to again complete the above-tracedoperating circuit for the operating magnet 53. At the end of the digitand when the dial embodied in the impulsing device 35 returns to normal,the indicated shunt springs are moved out of engagement to interrupt theoperating circuit for the magnet 53, thus permitting the ratchet andpawl mechanism associated with this magnet to advance the wiper 52 asecond step or into engagement with its associated second contact. Withthe wiper 52 in this position a circuit is completed for energizing thependulum type relay 65, this circuit eX- tending from the positivegenerator terminal I9 by Way of the winding of the relay 55, the secondContact of the contact set the wiper 52, the armature 54, and thewinding of the magnet 53 to the negative generator terminal 20. Due tothe relatively high resistance of the winding of the relay 65, themagnet 53 is insufciently energized over the circuit just traced tooperate. The relay 65, however, attracts its associated armature 66which, due to the weight carried by the free end thereof, starts tovibrate, intermittently to complete an obvious circuit for energizingthe slow-to-operate relay 65. After a predetermined and substantiallyxed time interval, the vibration of the weighted armature 65 dies outand this armature settles into engagement with its associated workingcontact, thereby to maintain the relay 50 continuously energized. Ashort time interval thereafter, the slow-to-operate relay 60 operates tocomplete at its armature 6| an obvious alternative circuit forenergizing the magnet 53. This magnet now operates to condition theassociated ratchet and pawl mechanism to step the wiper 52 a third stepand to open at its armature 54 the above-traced circuit for energizingthe relay 65. As a result, the two relays, 35 and 55, sequentiallyrestore in the order named, the last-mentioned circuit thereof,functioning to open at its armature 6| the alternative circuit forenergizing the magnet 55. When the magnet 53 is deenergized, the wiper52 is advanced to its third oir-normal position and the armature 54 isreleased to re-complete the abovetraced operating circuit for the relay65. Since the second to eighth contacts of the contact set 5| aremultipled together, the cycle of operations just described and involvingthe two relays Bl) and 65 and the magnet 53, is repeated seven times.When the wiper 52 is stepped to its ninth oir-normal position or intoengagement with its associated ninth contact, a circuit is completed forenergizing the relay '|0, this circuit extending from the positivegenerative terminal I9 by way of the winding of the relay 10, thearmature 44, the ninth contact of the contact set 5|, the wiper 52, thearmature 54, and the winding of the magnet 53 to the negative generatorterminal 2%. Due to the relatively high resistance of the winding of therelay 10, the magnet 53 is insuiiiciently energized to operate when thecircuit just traced is completed. The relay 10, however, operates toopen at its armature the previously traced holding circuit for the relay30, causing the lastmentioned relay to restore. Upon restoring, therelay 30 opens, at its armature 3|, the circuit for energizing thesignal lamp 23, and interrupts, at its armature 33, the circuit overwhich the contactor 25 is being held energized. The contactor 25 nowrestores to open the circuit over which the carrier current voltage ofthe alternator I5 is being impressed upon the carrier channel comprisingthe conductor lil and ground. The relay 1G, upon operating alsocompletes, at its armature 1|, an obvious alternative circuit forenergizing the magnet 53. This magnet in turn attracts its armature 54to open the operating circuit for the relay 'it causing this relay torestore and open the operating circuit for the magnet 53. The ratchetand pawl mechanism associated with -this magnet now advances the wiper52 into engagement with its associated tenth contact.

When the wiper 52 is stepped to its tenth cifnormal positon, a switchnormalizing circuit is completed for energizing the magnet 53. Thiscircuit may be traced as extending from the positive generator terminalI9 by Way of the armature 43, the multipled tenth to twenty-secondcontacts of the contact set 5|, the wiper 52, the armature 54, and thewinding of the magnet 53 to the negative generator terminal 20. Due tothe circuit interrupting action of the armature 54, the magnet 53 isrepeatedly energized over the circuit just traced to cause the wiper 52to be driven toward its home position. Since the twenty-fourth contactof the contact set 5| is connected directly to the positive generatorterminal I9 and the twenty-third contact of the Contact set 5| isconnected to this generator terminal over a path including the restoredarmature 42 of the relay 40, the stepping operation of the switch 50occasioned by energization of the magnet 53 over the normalizing circuitjust traced, continues until the wiper 52 is returned to its homeposition. When this occurs the switch normalizing circuit isinterrupted. Also, when the wiper 52 is disengaged from the multipledsecond to eighth contacts of the contact set 5|, the operating circuitfor the relay 65 is interrupted. Accordingly, the two relays 65 and 60are deenergized. Thus, all of the relays embodied in the transmittershown in Fig. 1 of the drawings are restored to normal. When theattendant observes the deenergized condition of the signal lamp 23 he isinformed that the desired control operation has been completed and hemay then restore the start key 2| to its normal position to arrest theoperation of the motor and the generators I6 and |8 driven thereby.Also, when the start key 2| is returned to normal, the operating circuitfor the signal lamp 22 is interrupted and this lamp is deenergized.Thus, the transmitter is fully released.

When the carrier current voltage is removed from the carrier channelcomprising the conductor t0 and ground, the relay 85 embodied in thereceiver illustrated in detail in Fig. 2 is deenergized and restores. Inasimilar manner the corresponding relays embodied in the other receiverscoupled to the carrier channel also restore. Upon restoring, the relayinitiates the sequential restoration of the relays 91, |30, |40, and |50in an obvious manner. With the two relays El and |50 deenergized, theoperating circuit for the contacter 95 is interrupted causing thiscontactor to open, at its armature 9B, the operating circuit for themotor 80. Accordingly, operation of the moto-r 88 and the two generators81 and 89 are arrested. When the relay |50 restores, it opens, at itsarmature |52, a point in the common portion of the operating and holdingcircuits for the three relays |10, |80, and |90 causing any operatedones of these relays to restore. Upon restoring, the relay |50 alsofunctions to interrupt at its armature |54 the abovetraced operatingcircuit for the control device 200, whereby the last-mentioned device isreleased to interrupt the secondary carrier current circuit 79. At itsarmature |5|, the relay |50, upon restoring, completes an alternativecircuit for energizing the motor magnet 4 of the switch |55, thiscircuit extending from the positive generator terminal 0| by way of thearmature I 3| the armature |5|, the multipled rst to tenth contacts ofthe contact set |00, the wiper ||0, the armature I6 and the winding ofthe magnet H4 to the negative generator terminal 92. Due

to the circuit interrupting action of the armature H6, the motor magnet||4 operates buzzer fashion rapidly to return the wipers of the switch|05 to their respective normal position at which time the off-normalsprings ||5 are opened. When the wiper is returned to its normalposition, the switch normalizing circuit just traced and including thearmature IIB is interrupted. Thus, the wipers of the switch are leftstanding in their respective normal positions. In connection with therestoration of the switch |65 to normal, it will be noted that theswitch normalizing circuit is initially completed substantiallysimultaneously with the deenergization of the driving motor 88 for thegenerator 89. Due to the mechanical inertia of the moving system drivenby the motor 88, however, the voltage developed by the generator 89 issuflicient to enable the switch normalizing operation of the rotaryswitch |65 to be fully effected before the voltage of the generator 89drops to an abnormally low value.

Although the release of the receiver shown in detail in Fig. 2 has alonebeen considered, it will be understood from the description pertainingto this receiver that the other receivers coupled to the carrier channelare restored to normal in an identical manner.

In the event the dispatcher attending the transmitter shown in Fig. 1desires to cause a switching unit associated wtih one of the secondarycarrier channels to be operated to the open circuit position, the key 28is actuated to its off-normal position instead of the key 21 followingoperation of the start switch 2l. For eX- ample, if the dispatcherdesires to energize the control device or switching unit controlled overthe secondary carrier circuit 19, to cause this device to be operated toits open circuit position, he will rst operate the start switch 2| toits offnormal position to initiate the operation of the transmitter andthe receivers in the manner previously described. A short time intervalthereafter, the key 23 is operated to its off-normal position tocomplete an obvious circuit for energizing the relay 4B. The relay 4|)performs the same operations as are described above with reference tothe relay 3D, i. e., it completes at its armature 4t the previouslytraced circuit for energizing the contactor 25, prepares at its armature41 the circuit for energizing the operating magnet 53 of the switch 50and completes at its armature 45 a holding circuit for itself. Inaddition, the relay 40 completes at its armature 4| an obvious circuitfor energizing the signal lamp 24, opens at its armature 44 a point inthe previously traced operating circuit for the relay 10, and preparesat its armature 42 an alternative operating circuit for thelast-mentioned relay. At its armature 44, the relay 40 also impressespositive generator potential upon the ninth contact of the contact set5| embodied in the rotary switch 55, Finally, at its armature 43, therelay 40 disconnects positive generator potential from the multipledtenth to twenty-second contacts of the contact set 5| and connects thesemultipled contacts to the multipled contacts numbered from two to eightinclusive, of the indicated contact set. The purpose of the operationsjust described is to insure that the relay 1U will not be operated untilthe wiper 52 of the switch 5i] is moved, under the control of the relays60 and 85 and the operating magnet 53, over the associated contactsnumbered from two to twenty-two inclusive. Such movement of the wiper 52obviously requires a considerably greater time interval than thatrequired for movement of the wiper over the contacts numbered from twoto eight, inclusive, of the contact set 5|. This, of course, means thatcarrier current is maintained upon the carrier channel comprising theconductor lil and ground, for a considerably longer time interval thanin the case when the relay Si] was operated in response to operation ofthe key 21. Specifically, the arrangement is such that when the key 2lis operated to cause the operation of the relay 35, carrier current isconducted to the carrier channel for a period of ten seconds followingthe completion of the dialing operation; whereas when the key 28 isoperated to cause the operation of the relay 4B, carrier current isco-nducted to the carrier channel for 'twenty seconds following thecompletion of the dialing operation at the transmitter,

After the key 28 is operated to its off-normal position to perform thefunction just described, the impulsing device 35 is actuated in themanner previously explained and in accordance with the two digitsdesignating the secondary carrier circuit to be operated upon. Themanner in which the receivers associated with the carrier channelrespond to the carrier pulses is exactly the same as set forth abovewith reference to operation of the impulsing device 35 followingoperation of the key 21. Here again, since the vcircuit 'i9 is to becompleted, the control device 25) is energized over the previouslytraced circuit shortly following the conclusion of the second digit.Also, at the end of the second digit, sustained operation of the rotaryswitch 5D is maintained through the above-described interaction betweenthe operating magnet 53 and the two relays and 55. The steppingoperation of the rotary switch under the control of the indicated relayscontinues until the wiper of this switch is moved into engagement withthe ninth contact of the contact set 5|, at which time, a circuitindependent of the relays (it and E5 is completed for energizing theoperating magnet 53. This circuit extends from the positive generatorterminal i9 by way of the armature M, the ninth contact of the Contactset 5|, the wiper 52, the armature 54 and the winding of the magnet 53to the negative generator terminal 2|). Due the circuit interruptingaction of the armature 54, the magnet 53 in cooperation with itsassociated ratchet and pawl mechanism now operates rapidly to advancethe wiper 52 to its tenth off-normal position at which time the slowstepping of the wiper is continued under the control of the two relaysand 65. Thereafter, and when the wiper 52 is stepped into engagementwith its associated twenty-third contact, the above-mentionedalternative circuit is completed for energizing the relay l5, thiscircuit extending from the positive generator terminal |55 by way of thewinding of the relay l, the armature 42, the twenty-third contact of thecontact set 5|, the wiper 52, the armature 54, and the winding of themagnet 53 to the negative generator terminal 2li. crates, it initiatesthe release of the transmitter and of the various receivers coupled tothe carrier channel in the exact manner previously described. Duringthis release of the apparatus, the control device 29E) is deenergized tointerrupt at its armature Ztl, the selected secondary carrier currentcircuit i9. Also, during the release of the apparatus and when the relayl0 operates, the holding circuit for the relay 4t is interrupted Whenthe relay l0 opcausing the last-mentioned relay to restore to open theoperating circuit for the signallamp 24 and tor restore the normalcircuit connections associated with the contact bank of the rotaryswitch 50. Upon operating,` the relay also completes the previouslytraced alternative circuit for energizing the magnet 53, whereby thismagnet is caused to restore the wiper 52 to normal and the relays 10, 6Uand 65 are released.

As previously indicated, the error key 'l5 is provided for the purposeof rapidly normalizing the apparatus in the event the dispatcher, afterpartially performing a circuit control selecting operation, discovers anerrorV in his procedure. For example, if the dispatcher discovers, afterdialing the rst digit of a circuit designating number, that he hasdialed the wrong digit or that he has operated the wrong one of the twokeys, 21 and 28, he may operate the error key 'l5 and cause theapparatus to be restored to normal before any of the secondary carriercurrent circuits have been affected. When the key 'i5 is operated to itsoff-normal position, positive generator potential is impressed by way ofthe switch springs 'I6 and l1 directly upon the rst and the multipliedsecond to eighth contacts of the contact set 5|. Also, if the relay 4Uis the operated one cf the two relays 30 and 40, positive generatorpotential is impressed by way of the springs 11 upon the multipliedtenth to twenty-second contacts of the contact set 5|. Alternatively, if

the relay 353 is the operated one of the two re-` lays 30 and 40,positive generator potential is impressed upon the last-mentionedcontact multiple over the previously traced path, including the restoredarmature 43 of the relay 40. Immediately the above described paths arecompleted, the operating magnet 53 of the switch 50 is energized overthe switch normalizing circuit including the circuit interruptingarmature 54. As a result, the wiper 52 is rapidly driven to its normalposition. During such movement of the wiper 52, one of the twopreviously traced circuits is completed for energizing the relay 1U,which relay upon operating, initiates the release of the apparatus inthe exact manner previously described.

The receiver shown in Fig. 2 is not claimed in this application.V It isclaimed in divisional application Serial No. 330,979 led April 22, 1940.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood that`various modicationsmay be made therein, and it is contemplated to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A control station for supplying control current to an associatedcontrol channel and comprising, in combination, a current source, acircuit for delivering current from said source to said channel, meansincluding an impulsing device for controlling said circuit to transmitcoded combinations of current pulses by way of said channel and forholding said circuit completed at the end of the pulse transmission,timingapparatus comprising a switch having a normal position andoperative to a number of off -normal positions, circuit means controlledby said im.- pulsing device for causing said switch to operate from oneposition to a succeeding position in response to each operation of saidimpulsing device to cause the transmission of a combination of currentpulses over said channel, means responsiveto the operation of saidswitch to a predetermined off-normal position for sustaining theoperation of said switchindependently of said impulsing device, andmeans responsive to the operation of said switch to a secondpredetermined ol-normal position for interrupting said circuit and forcausing said switch to be returned to its normal position.

2. A control station `for supplying control current to an associatedcontrol channel and comprising, in combination,` a current source, acircuit for delivering current from said source to said channel, meansincluding an impulsing deviceV for controlling said circuit to transmitcoded combinations of current pulses by way of said channel and forholding said circuit completed at the end of the pulse-transmission,timing apparatus comprising a stepping switch including an operatingmagnet, said switch having a normal position and being operative to anumber of off-normal positions, switch operating and normalizingcircuits for energizing said magnet, ccntacts controlled by saidimpulsing device for completing said operating circuit each time saidimpulsing device is operated to cause the transmission of a combinationof current pulses over said channel, relay means controlled by saidstepping switch and operative in response to operation of said steppingswitch to a predetermined off-normal position for periodicallycompleting said operating circuit, thereby to cause said stepping switchto be operated .to ya second off-normal position, and means responsiveto the operation of said switch to said second oil-normal position forinterrupting said first-named circuit and for causing said switchnormalizing circuit to be completed.

3. A control station for supplying control current to an associatedcontrol channel and comprising, in combination, a current source, acircuit for delivering current from said source to said channel, anelectromagnetic device for controlling said circuit, a normallyincomplete operating circuit for said electromagnetic device, a switch,a relay operative in response to operation of said switch to completesaid operating circuit, means including an impulsing device havingcontacts serially included in said operating circuit for interruptingand completing said operating circuit one or more times, thereby tocause current pulses to be transmitted by way of said channel, a holdingcircuit for said relay completed in response to opera-tion of saidrelay, timing apparatus comprising a switch having a number of operatingpositions andl operative from one position to a succeeding position inresponsev to each operation of said impulsing device, means responsiveto the operation of said last-named switch to a predetermined positionfor sustaining the operation of said last-named switch independently ofsaid impulsing device, thereby to cause said last-named switch to beoperated to a second predetermined position, and means responsive to theoperation of said lastnamed switch to said second predtermined positionfor interrupting said holding circuit, thereby to cause thesequential'restoration of said relay and said electromagnetic device. f

4. A control station for supplying control current to an associatedcontrol channel and comprising, in combination, a current source, acircuit for delivering current from said source to said channel, anelectromagnetic device for controlling said circuit, a. normallyincomplete operating circuit for said electromagnetic device, a

switch', a `relay operative in response to operation of said switch tocomplete said operating circuit, means including an impulsing devicehaving contacts serially included in said operating circuit forinterrupting and completing said operating circuit one or more times,thereby to cause current pulses to be transmitted by way of saidvchannel, a holding circuit for said relay completed in response tooperation of said relay, timing apparatus comprising a stepping switchincluding an operating magnet, said switch having a normal position andbeing operative to a number of ofi-normal positions, switch operatingand normalizing circuits for energizing said magnet, contacts controlledby said impulsing device for completingsaid switch operating circuiteach time said impulsing device is operated, relay means controlled bysaid stepping switch and operative in response to operation of saidstepping switch to av predetermined off-normal position for periodicallycompleting said switch operating circuit, thereby to cause said steppingswitch to be operated to a second off-normal position, and meansresponsive to the operation of said switch to said second oir-normalposition for interrupting said holding circuit, thereby to cause thesequential restoration of said relay and said electromagnetic device,and for causing said switch normalizing circuit to be completed.

5. Acontrol station for supplying control current to an associatedcontrol channel and comprising, in combination, a current source, acircuit for delivering current from said source to said channel, meansincluding an impulsing device for controlling said circuit to transmitcoded combinations of current pulses by way of `said channel andforvholding said circuit completed at the end of the pulse transmission,timing apparatus comprising a switch having a number of operatingpositions and operative from one position to a succeeding position inresponse to each operation of said impulsing device to cause thetransmission of a combination of current pulses over said channel, meansresponsive to the operation of said switch to a predetermined positionfor sustaining the operation of said switch independently of saidimpulsing device and at a predetermined speed, means responsive to theoperation of said switch to a second predetermined position forinterrupting said circuit, an error switch, and circuits controlled bysaid error switch for causing said rst-named switch to operate to saidswitch predetermined position at a substantially higher speed.

6. A control station for supplying control cur- C rent to an associatedcontrol channel and comprising, in combination, a current source, acircuit for delivering current from said source to said channel, a pairof switches, means responsive to operation of either of said switchesfor completing said circuit, means including an impulsing device forcontrolling said circuit to `transmit coded combinations of currentpulses by way of said channel and for holding said circuit completed atthe end of the pulse transmission, timing apparatus operative inresponse to operation of said impulsing device to cause the transmissionof a combination of current pulses over said channel, and meanscontrolled by said timing apparatus for interrupting said circuit aftera predetermined time interval which begins with the end of the pulsetransmission or for a longer time interval depending upon which of saidswitches is initially operated.

'7. A control station for supplying control curr rent to an associatedcontrol channel and comprising in combination, a current source, acircuit for delivering current from said source to said channel, a pairof switches, means responsive to operation of either of said switchesfor completing said circuit, means including an impulsing device forcontrolling said circuit to transmit coded combinations of currentpulses by Way of said channel and for holding said circuit completed atthe end of the pulse transmission, timing apparatus'operative inresponse to operation of said impulsing device to cause the transmissionof a combination of current pulses over said channel, means controlledby said timing apparatus for causing said circuit to be interrupted, andcircuit means jointly controlled by said first-named means and saidtiming apparatus for causing said last-named means to operate after apredetermined time interval which begins with the end of the pulsetransmission or for a longer time interval depending upon which of saidswitches is initially operated.

8. A control station for supplying control currentto an associatedcontrol channel and comprising, in combination, a current source, acircuit ior delivering current from said source to said channel, a pairof switches and relays individually controlled thereby, means responsiveto operation of either of said relays for completing said circuit, meansincluding an impulsing device for controllingr said circuit to transmitcurrentpulses by way of said channel and for holding said circuitcompleted at the end of the pulse transmission, timing apparatuscomprising a rotary switch including a set of contacts and a wiper forengaging said contacts, circuit means controlled by said impulsingdevice for initiating the operation of said rotary switch, an additionalrelay operative to cause said circuit to be interrupted, and a pair ofcircuits selectively prepared by one of said-iirst-named relays forenergizing said additional relay, one of said pair of circuits beingcompleted in response to a predetermined movement of said wiper oversaid contacts only when said one relay is deenergized and the other ofsaid pair of circuits being completed in response to a differentpredetermined movement of said wiper over said contacts only when saidone relay is energized.

9. A control station for supplying control current to an associatedcontrol channel and comprising, in combination, a current source, acircuit for delivering current from said source to said channel, a pairof switches and relays individually controlled thereby, means responsiveto operation of either of said relays for completing said circuit, means'including an impulsing device for controlling said circuit to transmitpulses by way of said channel and for holding said circuit completed atthe end of the pulse transmission, timing apparatus comprising a rotaryswitch including a set of contacts and a wiper for engaging saidcontacts, circuit means controlled by said impulsing device forinitiating the operation of said rotary switch, means controlled bymovement of said wiper over said contacts for sustaining the operationof said switch independently of said impulsing device, an additionalrelay operative to cause said circuit to be interrupted, and a pair ofcircuits selectively prepared by one of said rst-named relays forenergizing said additional relay, one of said pair of circuits beingcompleted in response to a predetermined movement of said wiper oversaid contacts only when said one relay is deenergized and the other ofsaid pair of circuits being completed in response to a differentpredetermined movement of said wiper over said contacts only when saidone relay is energized.

10. A control station for supplying selecting and control pulses to anassociated control channel and comprising, in combination, a circuit fortransmitting said pulses to said channel, means including an impulsingdevice for controlling said circuit to transmit a. plurality of codedcombinations of selecting pulses over said channel and to initiate thetransmission of a control pulse over said channel following thetransmission of said plurality of combinations of selecting pulses, atiming device having a plurality of settings and operative to a newsetting in response to each operation of said impulsing device to causethe transmission of a combination of selecting pulses over said channel,means responsive to the operation of said timing device to apredetermined setting for sustaining the operation of said timing deviceat a substantially constant rate, and means responsive to the sustainedoperation of said timing device to a second predetermined setting forcontrolling said circuit to terminate said control pulse.

HARRY E. HERSHEY.

